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  Java Practices -> Use Timer to schedule periodic tasks 
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<div class='page-title'>Use Timer to schedule periodic tasks </div>

<div class='main-body'>
 
<br>The <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Timer.html">java.util.Timer</a></tt>
and <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/TimerTask.html">java.util.TimerTask</a></tt>
classes can be used for many simple thread related tasks. Use them to perform
an action either periodically or just once. As well, the first execution
can be delayed to a specific time in the future.

<p>The general guideline is :
<ul>
<li>if it may take a long time, or may block, use a <tt>Thread</tt></li>
<li>if it is to be done later, or periodically, use <tt>TimerTask</tt> and <tt>Timer</tt> (which itself 
uses a background thread)  </li>
</ul>

<p><b>Example</b>

<p>Here, a task is performed once a day at 4 a.m., starting tomorrow morning.
<br>
<PRE>

<span class='keyword'>import</span> java.util.Timer;
<span class='keyword'>import</span> java.util.TimerTask;
<span class='keyword'>import</span> java.util.Calendar;
<span class='keyword'>import</span> java.util.GregorianCalendar;
<span class='keyword'>import</span> java.util.Date;

<span class='keyword'>public</span> <span class='keyword'>final</span> <span class='keyword'>class</span> FetchMail <span class='keyword'>extends</span> TimerTask {

  <span class='comment'>/**
  * Construct and use a TimerTask and Timer.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>void</span> main (String... arguments ) {
    TimerTask fetchMail  = <span class='keyword'>new</span> FetchMail();

    <span class='comment'>//perform the task once a day at 4 a.m., starting tomorrow morning
</span>    <span class='comment'>//(other styles are possible as well)
</span>    Timer timer = <span class='keyword'>new</span> Timer();
    timer.scheduleAtFixedRate(fetchMail, getTomorrowMorning4am(), fONCE_PER_DAY);
  }

  <span class='comment'>/**
  * Implements TimerTask's abstract run method.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>void</span> run(){
    <span class='comment'>//toy implementation
</span>    System.out.println(<span class='literal'>"Fetching mail..."</span>);
  }

  <span class='comment'>// PRIVATE ////
</span>
  <span class='comment'>//expressed in milliseconds
</span>  <span class='keyword'>private</span> <span class='keyword'>final</span> <span class='keyword'>static</span> <span class='keyword'>long</span> fONCE_PER_DAY = <span class='literal'>1000</span>*<span class='literal'>60</span>*<span class='literal'>60</span>*<span class='literal'>24</span>;

  <span class='keyword'>private</span> <span class='keyword'>final</span> <span class='keyword'>static</span> <span class='keyword'>int</span> fONE_DAY = <span class='literal'>1</span>;
  <span class='keyword'>private</span> <span class='keyword'>final</span> <span class='keyword'>static</span> <span class='keyword'>int</span> fFOUR_AM = <span class='literal'>4</span>;
  <span class='keyword'>private</span> <span class='keyword'>final</span> <span class='keyword'>static</span> <span class='keyword'>int</span> fZERO_MINUTES = <span class='literal'>0</span>;

  <span class='keyword'>private</span> <span class='keyword'>static</span> Date getTomorrowMorning4am(){
    Calendar tomorrow = <span class='keyword'>new</span> GregorianCalendar();
    tomorrow.add(Calendar.DATE, fONE_DAY);
    Calendar result = <span class='keyword'>new</span> GregorianCalendar(
      tomorrow.get(Calendar.YEAR),
      tomorrow.get(Calendar.MONTH),
      tomorrow.get(Calendar.DATE),
      fFOUR_AM,
      fZERO_MINUTES
    );
    <span class='keyword'>return</span> result.getTime();
  }
}
 
</PRE>
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction6407-2.html?Id=160'>Timers</a> <br>
 
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